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United States Patent |
6,016,603
|
Marando
,   et al.
|
January 25, 2000
|
Method of hydroforming a vehicle frame component
Abstract
A method for hydroforming a closed channel structural member that allows
the perimeter to be increased, but which maintains a relatively uniform
wall thickness throughout, includes the initial step of disposing a closed
channel structural member, such as a tube, within a first hydroforming die
defining a first die cavity. The inner surface of the first die cavity
corresponds in cross sectional shape to the outer surface of the tube, but
the perimeter of the first die cavity is somewhat larger than the
perimeter of the tube enclosed therein. A preliminary hydroforming
operation is then performed at a relatively high pressure to expand the
tube into conformance with the first die cavity. Throughout most of this
expansion, the outer surface of the tube does not engage the inner surface
of the die cavity. As a result, as the perimeter of the tube is increase,
the wall thickness thereof is decreased uniformly. The preliminarily
expanded tube is then disposed within a second hydroforming die defining a
second die cavity. The inner surface of the second die cavity corresponds
in cross sectional shape to the desired final shape for the tube. When the
second hydroforming die is closed, a final hydroforming operation is
performed at a relatively low pressure to deform the tube into conformance
with the second die cavity. Because the perimeter of the tube is
approximately equal to the perimeter of the second die cavity, the wall
thickness of the tube is unchanged by the final hydroforming operation.
Inventors:
|
Marando; Richard A. (Mohrsville, PA);
Sanko; Thomas R. (Hazleton, PA);
Schrack; Eric M. (Mohrsville, PA)
|
Assignee:
|
Dana Corporation (Toledo, OH)
|
Appl. No.:
|
076683 |
Filed:
|
May 12, 1998 |
Current U.S. Class: |
29/897.2; 29/421.1; 29/523; 72/61 |
Intern'l Class: |
B23P 011/02 |
Field of Search: |
29/897.2,897,897.3,421.1,523
72/58,61,62,370.22
|
References Cited
U.S. Patent Documents
Re33990 | Jul., 1992 | Cudini.
| |
4567743 | Feb., 1986 | Cudini.
| |
4744237 | May., 1988 | Cudini.
| |
4829803 | May., 1989 | Cudini | 72/61.
|
5097689 | Mar., 1992 | Pietrobon.
| |
5339667 | Aug., 1994 | Shah et al.
| |
5353618 | Oct., 1994 | Roper et al. | 72/58.
|
5363544 | Nov., 1994 | Wells et al. | 29/523.
|
5499520 | Mar., 1996 | Roper.
| |
5582052 | Dec., 1996 | Rigsby | 72/62.
|
5673470 | Oct., 1997 | Dehlinger et al. | 29/421.
|
5673929 | Oct., 1997 | Alatalo | 29/897.
|
Primary Examiner: Cuda; Irene
Assistant Examiner: Nguyen; Trinh T.
Attorney, Agent or Firm: MacMillan, Sobanski & Todd, LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application Ser.
No. 60/046,221, filed May 12, 1997.
Claims
What is claimed is:
1. A method of hydroforming a closed channel structural member comprising
the steps of:
(a) disposing the closed channel structural member within a die cavity of a
first hydroforming die defining a perimeter that is larger than the
perimeter of the closed channel structural member;
(b) performing a preliminary hydroforming operation to expand the closed
channel structural member into conformance with the die cavity of the
first hydroforming die such that the perimeter of the closed channel
structural member is increased;
(c) disposing the closed channel structural member within a die cavity of a
second hydroforming die defining a perimeter that is approximately the
same as the perimeter of the closed channel structural member; and
(d) performing a final hydroforming operation to deform the closed channel
structural member into conformance with the die cavity of the second
hydroforming die such that the perimeter of the closed channel structural
member remains approximately the same.
2. The method defined in claim 1 wherein said step (a) is performed by
providing the closed channel structural member with a shape that
corresponds with the shape of the die cavity of the first hydroforming
die.
3. The method defined in claim 2 wherein the closed channel structural
member has an outer surface defining a circular cross sectional shape, and
wherein the die cavity of the first hydroforming die has an inner surface
defining a circular cross sectional shape.
4. The method defined in claim 1 wherein said step (a) is performed by
supporting the closed channel structural member concentrically within the
die cavity of the first hydroforming die.
5. The method defined in claim 1 wherein the wall thickness of said closed
channel structural member is reduced during said step (b).
6. The method defined in claim 5 wherein the wall thickness of said closed
channel structural member is reduced substantially uniformly during said
step (b).
7. The method defined in claim 1 including the preliminary step of
pre-bending the closed channel structural member prior to disposing it
within a die cavity of a first hydroforming die.
8. The method defined in claim 1 wherein said step (b) is performed at a
relatively high pressure, and said step (d) is performed at a relatively
low pressure.
9. The method defined in claim 1 wherein step (d) is performed by providing
the closed channel structural member with a shape that corresponds with
the shape of the die cavity of the second hydroforming die.
10. The met hod defined in claim 9 wherein the closed channel structural
member has an outer surface defining a non-circular cross sectional shape,
and wherein the die cavity of the second hydroforming die has an inner
surface defining a non-circular cross sectional shape.
11. The method defined in claim 1 wherein the wall thickness of the closed
channel structural member is essentially unchanged during said step (d).
12. The method defined in claim 1 wherein at least a portion of the closed
channel structural member is deformed during said step (c).
13. A method of hydroforming a closed channel structural member comprising
the steps of:
(a) disposing the closed channel structural member within a die cavity of a
first hydroforming die defining a perimeter that is larger than the
perimeter of the closed channel structural member;
(b) performing a preliminary hydroforming operation to expand the perimeter
of the closed channel structural member into conformance with the die
cavity of the first hydroforming die;
(c) disposing the closed channel structural member within a die cavity of a
second hydroforming die defining a perimeter that is approximately the
same as the perimeter of the closed channel structural member; and
(d) performing a final hydroforming operation to deform the closed channel
structural member into conformance with the die cavity of the second
hydroforming die, whereby a wall thickness of the closed channel
structural member decreases during the preliminary hydroforming operation,
and whereby the wall thickness of the closed channel structural member
remains essentially constant during the final hydroforming operation.
14. The method defined in claim 13 wherein the die cavity of the first
hydroforming die has an inner surface defining a circular cross sectional
shape, and wherein the die cavity of the second hydroforming die has an
inner surface defining a non-circular cross sectional shape.
15. The method defined in claim 13 wherein at least a portion of the closed
channel structural member is deformed during said step (c).
Description
BACKGROUND OF THE INVENTION
This invention relates in general to methods for hydroforming closed
channel structural members to desired shapes, such as components for
vehicle frame assemblies. More specifically, this invention relates to an
improved method for hydroforming a closed channel structural member by
means of a two-stage process including (1) an initial relatively high
pressure hydroforming operation, wherein a portion of the member is
expanded to achieve a relatively small but essentially uniform wall
thickness, and (2) a subsequent low pressure hydroforming operation,
wherein a portion of the member is deformed into a desired shape while
maintaining the relatively small but essentially uniform wall thickness.
Many land vehicles in common use, such as automobiles, vans, and trucks,
include a body and frame assembly that is supported upon a plurality of
ground-engaging wheels by a resilient suspension system. The structures of
known body and frame assemblies can be divided into two general
categories, namely, separate and unitized. In a typical separate body and
frame assembly, the structural components of the body portion and the
frame portion are separate and independent from one another. When
assembled, the frame portion of the assembly is resiliently supported upon
the vehicle wheels by the suspension system and serves as a platform upon
which the body portion of the assembly and other components of the vehicle
can be mounted. Separate body and frame assemblies of this general type
are found in most older vehicles, but remain in common use today for many
relatively large or specialized use modern vehicles, such as large vans,
sport utility vehicles, and trucks. In a typical unitized body and frame
assembly, the structural components of the body portion and the frame
portion are combined into an integral unit that is resiliently supported
upon the vehicle wheels by the suspension system. Unitized body and frame
assemblies of this general type are found in many relatively small modern
vehicles, such as automobiles and minivans.
One well known example of a separate type of vehicular body and frame
assembly is commonly referred to as a ladder frame assembly. A ladder
frame assembly includes a pair of longitudinally extending side rails that
are joined together by a plurality of transversely extending cross
members. The cross members connect the two side rails together and provide
desirable lateral, vertical, and torsional stiffness to the ladder frame
assembly. The cross members can also be used to provide support for
various components of the vehicle. Depending upon the overall length of
the vehicle and other factors, the side rails of a conventional ladder
frame assembly may be formed either from a single, relatively long
structural member or from a plurality of individual, relatively short
structural members that are secured together. For example, in vehicles
having a relatively short overall length, it is known to form each of the
side rails from a single integral structural member that extends the
entire length of the vehicle body and frame assembly. In vehicles having a
relatively long overall length, it is known to form each of the side rails
from two or more individual structural members that are secured together,
such as by welding, to provide a unitary structural member that extends
the entire length of the vehicle body and frame assembly.
Traditionally, the various components of known vehicle body and frame
assemblies have been formed from open channel structural members, i.e.,
structural members that have a non-continuous cross sectional shape
(U-shaped or C-shaped channel members, for example). Thus, it is known to
use one or more open channel structural members to form the side rails,
the cross members, and other components of a vehicle body and frame
assembly. However, the use of open channel structural members to form the
various components of a vehicle body and frame assemblies has been found
to be undesirable for several reasons. First, it is relatively time
consuming and expensive to bend portions of such components to conform to
a desired final shape, as is commonly necessary. Second, after such
bending has been performed, a relatively large number of brackets or other
mounting devices must usually be secured to some or all of such components
to facilitate the attachment of the various parts of the vehicle to the
body and frame assembly. Third, in some instances, it has been found
difficult to maintain dimensional stability throughout the length of such
components, particularly when two or more components are welded or
otherwise secured together.
To address this, it has been proposed to form one or more of the various
vehicle body and frame components from closed channel structural members,
i.e., structural members that have a continuous cross sectional shape
(tubular or box-shaped channel members, for example). This cross sectional
shape is advantageous because it provides strength and rigidity to the
vehicle body and frame component. Also, this cross sectional shape is
desirable because it provides vertically and horizontally oriented side
surfaces that facilitate the attachment of brackets and mounts used to
support the various parts of the vehicle to the body and frame assembly.
In some instances, the various parts of the vehicle may be directly
attached to the vertically and horizontally oriented side surfaces of the
vehicle body and frame assembly.
In vehicle body and frame assemblies of this type, it is known that the
closed channel structural member may be deformed to a desired shape by
hydroforming. Hydroforming is a well known process that uses pressurized
fluid to deform a closed channel structural member into a desired shape.
To accomplish this, the closed channel structural member is initially
disposed between two die sections of a hydroforming apparatus that, when
closed together, define a die cavity having a desired final shape.
Thereafter, the closed channel structural member is filled with a
pressurized fluid, typically a relatively incompressible liquid such as
water. The pressure of the fluid is increased to a magnitude where the
closed channel structural member is expanded or otherwise deformed
outwardly into conformance with the die cavity. As a result, the closed
channel structural member is deformed into the desired final shape.
Hydroforming has been found to be a desirable forming process because
portions of a closed channel structural member can be quickly and easily
deformed to have a complex cross sectional shape. In those instances where
the perimeter of the closed channel structural member is essential the
same as the perimeter of the die cavity, the cross sectional shape of the
closed channel structural member is changed during the hydroforming
process. However, at least ideally, the wall thickness of the closed
channel structural member should remain relatively constant throughout the
deformed region. Hydroforming has also been found to be a desirable
forming process because portions of a closed channel structural member can
be quickly and easily expanded from a relatively small perimeter to a
relatively large perimeter. In those instances where the perimeter of the
closed channel structural member is somewhat smaller than the perimeter of
the die cavity, not only is the cross sectional shape of the closed
channel structural member changed during the hydroforming process, but the
wall thickness thereof is decreased. However, at least ideally, the wall
thickness of the closed channel structural member should decrease
uniformly through the expanded region.
In practice, however, it has been found that hydroforming can introduce
undesirable variations in the wall thickness of the closed channel
structural member. As mentioned above, the outer surface of the closed
channel structural member is deformed outwardly into engagement with the
inner surface of the hydroforming die during the hydroforming operation.
Because the inner surface of the hydroforming die is typically shaped
differently from the outer surface of the closed channel structural
member, one or more discrete portions of the outer surface of the closed
channel structural member will initially engage the inner surface of the
hydroforming die prior to engagement by the remaining portions thereof.
These initially engaging portions of the outer surface of the closed
channel structural member are frictionally locked in position at the
points of engagement because of the outwardly directed forces generated by
the high pressure hydroforming fluid. As a result, the remaining portions
of the closed channel structural member are stretched from the initially
engaging portions as the deformation of the closed channel structural
member is completed.
Such stretching results in undesirable variations of the wall thickness
variations throughout the perimeter of the closed channel structural
member. These wall thickness variations can be particularly acute when the
hydroforming operation not only deforms the perimeter of the closed
channel structural member, but also expands the magnitude of the perimeter
thereof. These wall thickness variations can result in undesirable
weaknesses in the formed closed channel structural member. One solution
would be to increase the wall thickness of the entire closed channel
structural member such that the most extreme reductions in the wall
thickness thereof would not adversely affect the overall strength of the
member for its intended use. However, such over-designing undesirably
increases the overall weight and cost of the closed channel structural
member and the resultant vehicle frame component. Thus, it would be
desirable to provide an improved method for hydroforming a closed channel
structural member that allows the perimeter thereto to be increased, but
which maintains a relatively uniform wall thickness throughout.
SUMMARY OF THE INVENTION
This invention relates to an improved method for hydroforming a closed
channel structural member that allows the perimeter thereto to be
increased, but which maintains a relatively uniform wall thickness
throughout. Initially, a closed channel structural member, such as a tube,
is pre-bent and disposed within a first hydroforming die defining a first
die cavity. The inner surface of the first die cavity preferably
corresponds in cross sectional shape to the outer surface of the tube
throughout some or all of the length thereof, but the perimeter of the
first die cavity is somewhat larger than the perimeter of the tube
enclosed therein. The tube is preferably supported concentrically within
the die cavity. Then, a preliminary hydroforming operation is then
performed at a relatively high pressure to expand the tube into
conformance with the first die cavity. Throughout most of this expansion,
the outer surface of the tube does not engage the inner surface of the die
cavity. As a result, as the perimeter of the tube is increase, the wall
thickness thereof is decreased uniformly. The preliminarily expanded tube
is then disposed within a second hydroforming die defining a second die
cavity. The inner surface of the second die cavity corresponds in cross
sectional shape to the desired final shape for the tube. When the second
hydroforming die is closed, a final hydroforming operation is performed at
a relatively low pressure to deform the tube into conformance with the
second die cavity. Because the perimeter of the tube is approximately
equal to the perimeter of the second die cavity, the wall thickness of the
tube is essentially unchanged by the final hydroforming operation.
Consequently, a relatively larger amount of such expansion can occur than
would normally be available if it was necessary to account for variations
in the wall thickness of the tube resulting from frictional engagement of
the tube with the first hydroforming die.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional elevational view of a closed channel structural
member disposed within a first hydroforming die prior to the commencement
of a preliminary hydroforming operation in accordance with the method of
this invention.
FIG. 2 is an enlarged sectional elevational view taken along line 2--2 of
FIG. 1.
FIG. 3 is a sectional elevational view of the closed channel structural
member and the first hydroforming die illustrated in FIGS. 1 and 2 after
the completion of the preliminary hydroforming operation.
FIG. 4 is an enlarged sectional elevational view taken along line 4--4 of
FIG. 3.
FIG. 5 is a sectional elevational view of the preliminarily deformed closed
channel structural member illustrated in FIGS. 3 and 4 disposed within a
second hydroforming die prior to the closing of the die sections and
commencement of a final hydroforming operation.
FIG. 6 is a sectional elevational view similar to FIG. 5 after the closing
of the die sections, but prior to the commencement of the final
hydroforming operation.
FIG. 7 is a sectional elevational view similar to FIG. 6 after commencement
of the final hydroforming operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, there is illustrated in FIGS. 1 and 2 a
closed channel structural member, such as a tube 10, that can be used in
conjunction with the method of this invention to form a vehicle frame
component or other desired article. The tube 10 is conventional in the art
and is preferably formed having a uniform wall thickness T.sub.1 through
the length thereof The tube 10 is disposed within a first hydroforming
die, indicated generally at 11, that is composed of a first die section 12
and a second die section 13. As is well known, the die sections 12 and 13
have respective cavity portions 12a and 13a formed therein that cooperate
to form a hydroforming die cavity when the die sections 12 and 13 are
moved into engagement with one another as shown. Although the method of
this invention will be explained and illustrated in conjunction with the
illustrated linearly extending tube 10, it will be appreciated that this
invention may be practiced with a tube that has been pre-bent, such as in
a conventional tube bending apparatus, to have one or more bends therein.
The inner surface of the die cavity of the first hydroforming die 11
preferably corresponds in cross sectional shape to the outer surface of
the tube 10 throughout some or all of the length thereof. Thus, in the
illustrated embodiment, the cross sectional shape of the die cavity of the
first hydroforming die 11 is circular throughout the length thereof,
corresponding in shape to the circular outer surface of the tube 10.
However, it is contemplated that the tube 10 and the first hydroforming
die 11 may have other cross sectional shapes as desired. As best shown in
FIG. 1, the perimeter of the central portion of the die cavity of the
first hydroforming die 11 is somewhat larger than the perimeter of the
tube 10. As will be explained in detail below, the perimeter of the tube
10 will be increased within this enlarged central portion of the die
cavity of the first hydroforming die 11. For reasons that will become
apparent below, the tube 10 is preferably supported concentrically within
the enlarged central portion of the die cavity of the first hydroforming
die 11.
FIGS. 3 and 4 show the tube 10 after the completion of a preliminary
hydroforming operation. The hydroforming operation is, of itself,
conventional in the art and uses pressurized fluid to deform and expand
the tube 10 into conformance with the die cavity of the first hydroforming
die 11. To accomplish this, the tube 10 is filled with a pressurized
fluid, typically a relatively incompressible liquid such as water. The
pressure of the fluid is increased to a magnitude where the tube 10 is
deformed outwardly into conformance with the die cavity. As a result, the
tube 10 is deformed into the shape illustrated in FIGS. 3 and 4. Any
conventional apparatus may be used to perform the preliminary hydroforming
operation.
As shown in FIGS. 3 and 4, the preliminary hydroforming operation is
effective to increase the perimeter of the central portion of the tube 10
to correspond with the perimeter of the central portion of the die cavity
of the first hydroforming die 11. Because of this, the wall thickness of
the central portion of the tube 10 is decreased to a wall thickness
T.sub.2 that is somewhat less than the original wall thickness T.sub.1.
Notwithstanding this reduction, the wall thickness of the central portion
of the tube 10 is essentially uniform not only circumferentially as shown
in FIG. 4, but also axially throughout most of the entire central portion
of the tube 10. This is because the tube 10 is expanded in substantially
the same cross sectional shape (circular in the illustrated embodiment) as
the cross sectional shape of the enlarged central portion of the die
cavity of the first hydroforming die 11. The wall thickness of the tube 10
will gradually increase at the junction between the central portion of the
tube 10 and the two ends thereof. In the illustrated embodiment, the ends
of the tube 10 remain in essentially their original condition and wall
thickness. However, it will be appreciated that such ends (or other
portions of the tube 10) may be deformed during this preliminary
hydroforming operation.
FIG. 5 illustrates the preliminarily expanded tube 10 disposed within a
second hydroforming die, indicated generally at 15, that is composed of a
first die section 16 and a second die section 17. As with the first
hydroforming die 11, the die sections 16 and 17 have respective cavity
portions 16a and 17a formed therein that cooperate to form a hydroforming
die cavity when the die sections 16 and 17 are moved into engagement with
one another. In FIG. 5, the die sections 16 and 17 are shown in the
process of being moved toward one another, as shown by the respective
arrows. Thus, only the opposed upper and lower portions of the expanded
tube 10 are shown as being engaged by the die sections 16 and 17. The
inner surface of the die cavity of the second hydroforming die 15
preferably corresponds in cross sectional shape to the desired final shape
for the tube 10. The cross sectional shape of the die cavity of the second
hydroforming die 15 can vary as desired throughout the axial length
thereof.
FIG. 6 illustrates the die sections 16 and 17 after being moved into
engagement with one another, but prior to the commencement of the final
hydroforming operation. As shown therein, the perimeter of the illustrated
portion of the die cavity of the second hydroforming die 15 is
approximately equal to the perimeter of the expanded tube 10. Thus, when
the two die sections 16 and 17 are moved into engagement with one another,
portions of the tube 10 may be deformed inwardly so as to fit completely
within the die cavity of the second hydroforming die 15 without being
pinched therebetween. Thereafter, a final hydroforming operation is
performed to complete the formation of the tube 10 into the finished
article. FIG. 7 shows the tube 10 after the completion of this final
hydroforming operation. As with the preliminary hydroforming operation
described above, the final hydroforming operation uses pressurized fluid
to deform and expand the tube 10 into conformance with the die cavity of
the second hydroforming die 15. The final hydroforming operation is
effective to deform the tube 10 to correspond in shape with the shape of
the die cavity of the second hydroforming die 15. However, because the
perimeter of the tube 10 is approximately equal to the perimeter of the
die cavity of the second hydroforming die 15, the wall thickness of the
tube 10 after the second hydroforming operation is completed is
essentially maintained at the wall thickness T.sub.2. If desired, the
interior of the expanded tube 10 may be lightly pressurized as the die
sections 16 and 17 are moved toward one another to resist collapsing and
cause the expanded tube 10 to conform to the shape of the die cavity.
Thus, it will be appreciated that the preliminary hydroforming operation is
effective to expand the tube 10 within the first hydroforming die, thereby
increasing the perimeter of the tube 10 while decreasing the wall
thickness thereof. Thus, the preliminary hydroforming operation is
preferably performed by supplying fluid at a relatively high pressure
within the tube 10. For the reasons set forth above, the initial expansion
of the circular cross section tube 10 within the circular die cavity of
the first hydroforming die 11 causes the reduction in the wall thickness
of the tube 10 to be substantially uniform. Consequently, a relatively
larger amount of such expansion can occur than would normally be available
if it was necessary to account for variations in the wall thickness of the
tube 10 resulting from frictional engagement of the tube 10 with the first
hydroforming die 11. This pre-expansion of the tube 10 further allows the
final hydroforming operation to be substantially limited to deformation of
the enlarged tube 10, wherein the perimeter and wall thickness of the tube
are substantially unchanged. During this final hydroforming operation, the
material forming the tube 10 merely slides into conformance with the die
cavity. Thus, the final hydroforming operation can be performed by
supplying fluid at a relatively low pressure within the tube 10. Thus, the
method of this invention permits greater expansion of the tube 10 and the
use of thinner wall thicknesses than has been previously attainable.
As mentioned above, the preliminary hydroforming operation is preferably
performed by supplying fluid at a relatively high pressure within the tube
10, expanding the material of the tube 10 to correspond with the shape of
the die cavity of the first hydroforming die 11. This relatively high
pressure expansion tends to eliminate springback in the formed tube 10.
The amount of pressure required to effect the initial hydroforming
operation is a function of several factors, including wall thickness,
yield strength, and minimum inside radius of the tube 10. The final
hydroforming operation is preferably performed by supplying fluid at a
relatively low pressure within the tube 10, deforming the material of the
tube 10 to correspond with the shape of the die cavity of the second
hydroforming die 15. This relatively low pressure expansion does not tend
to eliminate springback in the formed tube 10. However, because the final
hydroforming operation merely moves the material of the tube 10 to desired
locations, as opposed to expanding it, acceptable tolerances can be
maintained for the finished article.
In accordance with the provisions of the patent statutes, the principle and
mode of operation of this invention have been explained and illustrated in
its preferred embodiment. However, it must be understood that this
invention may be practiced otherwise than as specifically explained and
illustrated without departing from its spirit or scope.
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